Immobilization of facet-engineered Ag3PO4 on mesoporous Al2O3 for efficient industrial waste gas purification with indoor LED illumination

The immobilization of a photocatalyst on a proper support is pivotal for practical environmental applications. Herein, as a rising visible light photocatalyst, different facet-engineered Ag3PO4{111}, Ag3PO4{110}, Ag3PO4{100} and irregular Ag3PO4 were first immobilized on mesoporous Al2O3, then applied for photocatalytic removal of ppm-leveled NO under visible light illumination. Photocatalytic performances for NO removal by these immobilized Ag(3)PO(4 )were found to be highly facet-dependent, showing the degradation kinetics in the order of Ag3PO4{111} tetrahedra > Ag3PO4{110} rhombic dodecahedra > Ag3PO4 {100} cubes > irregular Ag3PO4. The density functional theory (DFT) calculations were used to investigate the difference in the catalytic activity of Ag3PO4/Al2O3 with exposed {111}, {110}, and {100} facets. The experimental characterization and theoretical calculations all confirm that the {111} facets with high surface energy can not only facilitate adsorption/activation of O-2 and H2O but also be beneficial to the generation of center dot O-2(-) and center dot OH radicals, which result in significantly enhanced activity for NO oxidation. A modified band diagram showing different degrees of band edge bending can explain these observations. A reaction pathway study based on both in situ FT-IR and molecular-level simulation of NO adsorption and transformation indicates that this Ag3PO4 {111}/Al2O3 can efficiently adsorb NO and transform it into harmless nitrate products via NO -> NO+ and NO2+-> nitrate or nitrite routes. The present work reveals the facet-dependent radical formation mechanisms of Ag3PO4/Al2O3, and also provides new perspectives for promoting environmental applications of immobilized photocatalysts.